1. Field of the Invention
The present invention relates to an aqueous ink having an extended cap-off time and a process for manufacturing the ink.
2. Description of the Related Art
The ink is particularly an ink for writing, drawing, painting, printing or marking on normal paper or other absorbent writing carriers. The ink is particularly intended for use in fountain pens, ballpoint pens or stencil writers, in so-called felt-tip pens or pencils, in ink jet systems and/or in other capillary duct writing devices or systems.
Off-time is understood to be the time period over which a writing device or writing system may remain open, i.e., with the cap off, stored or unused without drying.
Aqueous inks are known in principle and usually contain water as solvent and pigments or water-soluble dyes as coloring agents. They usually additionally contain additives, such as tensides, emulsifying agents, preservatives, moist-keeping agents and/or glycols.
The principal disadvantage of these inks is their usually very short cap-off time when used, for example, in felt-tip pens, these usually aqueous dye-type inks dry up already after a very short period of time, i.e., usually within a few hours, if they are not closed in an air-tight manner by a protector.
The dye additionally frequently crystallizes at the tip or nozzle and clogs the tip or nozzle. Even if such pens or nozzles are closed again later, the pen or push button usually cannot regenerate again. Even after a relatively short period with the cap off, most of these conventional devices have a poor start-up or break-in behavior or do not work at all with such inks, or they must be reactivated possibly by very long start-up attempts, unless they are not already completely useless.
Various solutions have been proposed for increasing the cap-off time or for improving the drying-up behavior of such inks.
For example, DE-PS 530 800 describes a quick-drying writing liquid which does not dry up in the pen and in the writing device, wherein the liquid, in addition to volatile components, such as alcohols, etc., is supposed to contain organic acid esters of glycerin or glycol in order, on the one hand, to effect a quick drying of the writing on the paper and, on the other hand, to prevent quick drying within the writing device.
In accordance with DE-AS 19 13 174, an ink preparation on an aqueous basis is also supposed to contain an organic vehicle, or a special alkyl amide, in order to prevent or delay drying within a porous pen tip.
DE-PS 39 41 662 discloses a writing liquid in the form of an ink on an aqueous basis to which are added special polyglycol ethers in order also to reduce or delay drying of the ink in the writing device.
EP-PS 359 805 proposes the use of solids as antiblock additives for marking liquids in order to provide an evaporation-retarding closure for effectively preventing drying of the ink in unprotected or unused capillary outlet openings of writing devices or nozzles. To be considered as such soluble solids are, among others, inorganic salts, organic salts or other organic compounds, amino acids, urea, sulfur compounds, etc.
In addition, JP-P/AS 6-47 660 describes an ink having an increased cap-off time which can be stored over a long period of time without protector. This ink is composed of a dye, an organic solvent, resin, decaglycerin and a-olefin (alpha-olefin).
Olefin is the group designation for acyclic and cyclic aliphatic hydrocarbons with one or more reactive double bonds in the molecule. When the ink contains a-olefins, the double bond is between the first and second carbon atom and the ink is highly reactive because of its unsaturated character. The disadvantage of this ink is the presence of the a-olefins which may have the result that the ink is not stable during storage because of reactions of the a-olefin with other ink components.
All other proposed solutions have the additional disadvantage that, in the same manner as other commercially available recipes with basic dyes and ethylene glycol which actually also usually have a good cap-off time, the use of the raw materials is not necessarily safe with respect to their toxicological and physiological properties and may lead to problems when used in the end products, particularly by children.